Photoluminescent Lanthanide-Organic Bilayer Networks with 2,3-Pyrazinedicarboxylate and Oxalate
2010; American Chemical Society; Volume: 49; Issue: 7 Linguagem: Inglês
10.1021/ic902522j
ISSN1520-510X
AutoresP.C.R. Soares-Santos, Luís Cunha‐Silva, Filipe A. Almeida Paz, Rute A. S. Ferreira, João Rocha, Luís D. Carlos, Helena I. S. Nogueira,
Tópico(s)Magnetism in coordination complexes
ResumoThe hydrothermal reaction between lanthanide nitrates and 2,3-pyrazinedicarboxylic acid led to a new series of two-dimensional (2D) lanthanide-organic frameworks: [Ln2(2,3-pzdc)2(ox)(H2O)2]n [where 2,3-pzdc2− = 2,3-pyrazinedicarboxylate, ox2− = oxalate, and Ln(III) = Ce, Nd, Sm, Eu, Gd, Tb, or Er]. The structural details of these materials were determined by single-crystal X-ray diffraction (for Ce3+ and Nd3+) that revealed the formation of a layered structure. Cationic monolayers of {∞2[Ln(2,3-pzdc)(H2O)]+} are interconnected via the ox2− ligand leading to the formation of neutral ∞2[Ln2(2,3-pzdc)2(ox)(H2O)2] bilayer networks; structural cohesion of the crystalline packing is reinforced by the presence of highly directional O−H···O hydrogen bonds between adjacent bilayers. Under the employed hydrothermal conditions 2,3-pyrazinedicarboxylic acid can be decomposed into ox2− and 2-pyrazinecarboxylate (2-pzc−), as unequivocally proved by the isolation of the discrete complex [Tb2(2-pzc)4(ox)(H2O)6]·10H2O. Single-crystal X-ray diffraction of this latter complex revealed its co-crystallization with an unprecedented (H2O)16 water cluster. Photoluminescence measurements were performed for the Nd3+, Sm3+, Eu3+, and Tb3+ compounds which show, under UV excitation at room temperature, the Ln3+ characteristic intra-4fN emission peaks. The energy level of the triplet states of 2,3-pyrazinedicarboxylic acid (18939 cm−1) and oxalic acid (24570 cm−1) was determined from the 12 K emission spectrum of the Gd3+ compound. The 5D0 and 5D4 lifetime values (0.333 ± 0.006 and 0.577 ± 0.017 ms) and the absolute emission quantum yields (0.13 ± 0.01 and 0.05 ± 0.01) were determined for the Eu3+ and Tb3+ compounds, respectively. For the Eu3+ compound the energy transfer efficiency arising from the ligands' excited states was estimated (0.93 ± 0.01).
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